Television transmitter



June .20, 1939 K. scHLl-:slNGER 2,153,215

TELEVISION TRANSMITTER Filed April 5, 1935 v AMA Patented June 20, 1939 UNITED STATI-:s

TELEVISION TRANSMITTER Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, 'Berlin- Steglitz, Germany Application April 5,

1935, Serial No. 14,846

In Germany April 6, 1934 3 Claims.

The present invention relates to television transmitters which, on the same wave with the video signals, transmits synchronisation impulses. As Wellknown, it is necessary in transmitters of this `kind that the synchronisation impulses exceed toa certain extent the highest amplitudes ofthe video current, so that at the receiver a proper separation of synchronisation and video signals by means of an amplitude filter will be possible.

. It-has been proposed to ensure the said condition on .the high frequency side of the transmitter by modulating e. g. the antenna current by the video signals so that it never decreases under a certain minimum value. The aerial. current disappears entirely only when the aerial is disconnected from Vthe high frequency generator by a switch operated by the synchronisation signals, the requirement that thesesignals possess an overwhelming amplitude as compared with' the image` signals thus being complied with.

VAccording to the invention the correct amplitude ratio of video and synchronizing signals is already ensured on the low frequency side, i. e. prior to the entry of the modulating potentials into thehigh-.frequency transmitter. It has already 'been shown in the application Ser. No. 725,743 in what manner a .low-frequency mixing of the image signals and the synchronisation signals `in this way may be brought about, for example by producing the synchronisation signals electrically .by means of a special impulse connectionand performing an electrical mixing at the output of vthe image current amplifier. The present application sets forth a special method in order to prevent the image potential peaks from becoming occasionally equal to or greater than the synchronisation peaks. The application accordingly relates to the combination of amplitude lirnitingimeans operating without inertia for the image .current amplifier with the method previously set forth in the application Ser. No. 712,971 for the low-frequency mixing of synchronisation and image signals.

by means of the accompanying drawing, in which Fig. 1 shows the general scheme of a transmitteraccorcling to the invention, whilst Fig. 2 shows a more detailed connection diagram.

Fig. 1 shows by way of example a transmission arrangement with low-frequency mixing. In the same I is the Nipkow disc of the transmitter, whiohscans the image in the known fashion and controls the image current amplier 3 through the medium of a-.photo-cell 2, ywhilst a second photo-Celli behind-a separate ring of apertures receives the line frequency. The latter is passed to a special impulse apparatus 5 which, as already described in detail in the application No,

,The invention will be more clearly explained 725,743, and the construction of which is moreover not essential for comprehension of the present application, furnishes the lead 6 with signals of constant amplitude (for example 30 volts), constant direction (preferably negative, i. e. in the image black) and constant duration (for example 5% of the line period), The two outputs, i. e. the leads 6 and 1, the latter being the output of the video current amplifier 3, are connected to the input of a common vhigh frequency transmitter 8. If the unmodulated aerial current is equal to half the maximum value the controlling voltage furnished by the amplifier 3 must obviously full the following conditions:

1. In the negative direction it should never surpass a certain value lowering the antenna current to say 20% of its maximum amplitude. If .it exceeds this amount, the amplitude lter of the receiver is no longer able to perform a reliable separation of the signals, and the synchronism is instantly destroyed.

2. In the positive directionit should not surmount the control range of the transmitter.

3. When employing films withrapidly varying transparency there should be provided a special regulating device which compensates electrically the variable light conditions, modulating or strengthening Ythe contrasts of the image.

4. The device referred to under l should be capable of being adjusted and of operating independently of the devices referred to under 2 and 3.

Fig. 2 shows a form of embodiment of the peak value device according to the invention. In the train of the low frequency amplifier 3 there are shown a penultimate and a final amplifier tube 9 and I0 coupled by means of anode resistance I5 and condenser'l. Negative signals at the amplifier output 'I indicate positive signs at the grid of thenal amplier tube Iii. At this point, in accordance with the invention, there is connected through the medium of a coupling condenser II a potential limiter consisting of a discharge tube I4, the anode of which is supplied with an adjustable bias of negative sign I3 over a series resistance I2. The tube I4 is preferably a gaslled diodeV with small inner resistance, i. e., with high emission and small inner spacing. When the vpotential of the grid of the tube IIJ surpasses that of I3 the emission of I4 accordingly occurs very suddenly. The limiting eifect of the arrangement is improved by a series resistance 23. 23 should be small as compared with the capacitative input resistance of the tube I Il at the maximum image frequency, but large as compared with the discharge resistance of the tube I4. The signals, therefore, at the amplifier output 'I are unable to proceed beyond a negative surge value, the height of which may be adjusted by adjustment of the bias I3.

As regards the dimensioning of the coupling means II-I2 a time constant of approximately 10-2 seconds is desirable which is obtained by choosing 11 to .1 mf. and 12 to about .1 megohm.

The latter resistance is relatively large in com-1.

parison to the anode resistance I5 of approximately 5000 ohms. y Y j It is not suiiicient to ensure that the negative peak values are constant if at the same time the` degree of amplification of 3 has been incorrectly adjusted. If the amplifier is set to be too sensitive, it may occur for example that its output Yoscillation is already cut off proceeding from the centre. All values below the middle grey down to black would be made equal in the image, so that corresponding contours would not be visible at all. .The applicant has already set forth in the application No. 725,743 that upon the transmission care requires to be taken by means of an automatic regulator that the frequently occurring considerable fluctuations in the transparency of the lm and the copying brilliancy are intercepted. In addition to these conditions it is necessary that this peak value regulator regulates only the opposite amplitude of the signals not already limited by the tube I4. A regulating tube of this character, operating a directional amplier, is designated I1, its anode potential source I8, its anode resistance I9, its grid bias regulator 22. From the point 20 a regulating lead passes to the grid of the tube 9. The grid of the tube I1 is connected with Ya point, the potential of which has a phase of displacement of towards point I6, preferably by Way of the condenser 2I with the output lead 1. In this connection system there is not only obtained an adjustment of the amplier 3, regulable by the potentiometer 22, to an always constant medium output potential, but at the same time there is avoided an over-control into positive. The requirements 2 and 3 are accordingly fullled.

I claim:

l. In a television transmission arrangement comprising means for transforming the Vpicture vto be transmitted into picture contents currents,

means for generating synchronisation signals having a constant amplitude exceeding the greatest amplitude of said picture contents currents, two electronic ampliers for amplifying said picture contents currents and said synchronisation signals, said electronic amplifiers containing a plurality of electronic valves, means for coupling the stages of said electronic amplier with one another, means for mixing the output potentials of said two amplifiers, means for generating an ultra-short carrier wave and means for modulating said mixture onto said ultra-short carrier wave, a limiting device comprising a gas-lled discharge tube having anode and cathode, a D. C.

potential source, a resistance and a condenser,

saidanode of said discharge tube being connected by means of said condenser to the input of one of said amplifier valves of said picturecurrent aniplier, said D. C. potential source and said resistance connected in series across the discharge space oi said discharge tube, said D. C. potential source being so adjusted as to limit the output potential of said picture current amplifier asV not to exceed a pre-determined value below the constant output potential of said synchronising signal amplifier.

2. In a television transmission arrangement comprising means for transforming the picture to be transmitted into picture contents currents, means for generating synchronisation signals having a constant amplitude exceeding the great- ,est amplitude of said picture contents currents,

two electronic ampliers for amplifying said pic- 'j turecontents currents and said synchronisation signals, said electronic amplifiers containing a plurality of electronic valves, means for coupling the stages of said electronic amplier with one another, means for mixing the output potentials of said two amplifiers, means for generating an ultra-short carrier wave and means for modulating said mixture onto said ultra-short carrier wave, a limiting device comprising a gas-iiled discharge tube having anode and cathode, a D. C. potential source, resistance and a condenser, said anode of said discharge tube being connected by means of said condenser to the input ofone of said ampliervalves of said picture current ampliiier, said D. C. potential source and said resistance connected in series across the discharge space of said discharge tube, said D. C. potential source being so adjusted as to limit the ouput potential of said picture current amplier as not to exceed a pre-determined value below the constant output potential of said synchronising signal amplier, and a regulating device connected to the output of said picture curret amplier for regulating the amplication degree of said picture current amplifier as to give a iixed potential range-for the khighest and lowest amplitudes of the output potential of said picture current` ampliiier. l

1 3. In a television transmission arrangement comprising means for transforming the picture to be transmitted into picture contents currents. means for generating synchronisation signals having a constant amplitude exceeding the greatest amplitude of said picture contents currents, two electronicampliers for amplifying said picture contents currents andsaid synchronisation signals, said electronic ampliers containing a plurality of electronic valves, means for coupling the stages of said electronic ampliler with one another, .means for mixingthe output potentials of said two amplifiers, means for generating an ultra-short carrier wave and means for modulating said mixture onto said ultra-short carrier wave, a limiting device comprising a gas-illled discharge tube having anode and cathode, a D. C. potential source, resistance and a condenser, said anode of said dischargetube being connected by means Yof said condenser to the input of one of said amplifier valves of said picture current ampliiier, said D.'C. potential source and said resistance connected in series across the discharge space of said discharge tube, said D. C. potential source being so adjusted as to limit the output .the potential of said picture current amplier as not to exceed a pre-determined value below Ythe constant output potential of said synchronissaid limiting device independent of an adjust- 70,

ment of saidv regulating device.

' Y l KURT SCHLESINGER... 

